Stents are prostheses which may be made out of metal and may be either balloon expandable or self expandable, or which may be made out of a polymer. Stents are used for scaffolding or dilatation of diseased segments in hollow organs, particularly in blood vessels, which may be applied by use of catheter techniques, as used in heart catheterization and angioplasty procedures. Stents are made of wire-like materials or cut from tubes by laser cutting techniques or other techniques such as etching. The wire-like mesh forming the tubular wall of the stents includes struts (stent material) and gaps between the struts (no material). The struts usually exhibit an alternation of sinus wave shapes in circumferential extension and sinus wave shapes in longitudinal extension, or a diamond shaped configuration, or a combination of different shapes.
If a lesion is located in or near a bifurcation of a vessel, i.e. at the origin of a side branch taking off from a main branch, a balloon angioplasty procedure may be performed and a stent may be placed after the dilatation in the dilated segment in order to maintain acute and late vessel patency by scaffolding the dilated segment either permanently or over a period of time (e.g. via use of a bioabsorbable stent). The stent may be further coated with a drug for inhibition of restenosis development. The stent may also be placed as primary treatment without prior balloon dilatation or catheter based pre-treatment methods. The stent must cover the target lesion completely, and in some cases should even reach beyond the diseased segment into the adjacent non-diseased or less diseased vessel areas, in order to fully use the potential of the stent for acute and late vessel patency. Thus, in the case of a bifurcation, the stent must cover the ostium of the side branch. The ostium of a side branch often has a cross-sectional plane which does not run perpendicular to the longitudinal axis of the side branch, as the side branch may take off at an angle other than 90°, such as at an angle between 40°-60°. Conventional stents may not adequately provide coverage in such circumstances.
Various solutions for bifurcation or ostial stents and catheters for delivery of such stents have been disclosed. US Patent Publication 20050222672 to Shmulevitz discloses a self expandable stent, covered with a retractable sheath for compression of the stent, with a stem portion and a cap portion. The stent has flared ends and a toroidal shape for introduction into the main branch, and for overlapping the carina of the vessel branching area into the side branch.
Similarly, US Patent Publication 20050154447 to Goshgarian discloses a self expandable stent with flared ends. A dual balloon implantation method is used to implant the balloon expandable stent into an ostium. In order to increase the diameter of the ostial opening of the stent, i.e. to flare the ostial stent portion, one balloon of the dual balloon system is used.
The above-referenced disclosures fail to disclose using a single stent that fits the bifurcation anatomy without protrusion of a portion of the stent from the side branch into the main branch or from the main branch into the side branch. Rather, they disclose protrusion portions and/or the use of stent assemblies or multiple stents combined.
Moreover, if two stents are needed for treatment of a lesion in the main branch, with the necessity of bridging the ostium of the side branch, the protruding portions of the stents may lead to metal overlap, collision and stent strut distortion. This may reduce the acute and late (long term) chances of procedural success, as well as lead to immediate complications, such as an increased risk for thrombosis in the stents.
U.S. Pat. No. 6,682,556 to Ischinger discloses a catheter for placement of an oblique stent into a side branch. However, Ischinger does not disclose a specific design of an oblique stent which can be used to meet the requirements of successful bifurcation stent treatment.
There is thus a need for a stent which upon expansion has at least one oblique end, wherein the stent design and architecture are suitable for providing such oblique end, and wherein the stent may be successfully used to treat a bifurcated vessel.